A typical example of a radio frequency switching semiconductor device is a PIN diode. A simplified electrical model for such a device in the forward biased mode consists of a resistor and inductor in series (Rs and Lp). The isolation of such a switch is a function of the net impedance (R+jwX). At high frequencies, the series inductance (Lp) is usually the limiting factor for device isolation in common leaded and surface mount devices (SMD).
In FIG. 1, a schematic diagram illustrating the electrical parasitics associated with a conventional PIN diode package, such as the industry standard SOT-23 package is shown. The PIN diode package consists of an anode side 102 and a cathode side 118. Starting at the anode side 102 there is shown a leadframe inductance 104 attributed to the anode side leadframe, which has a typical inductance value of approximately 0.3 nH. A wirebond inductance 108 is formed by the wirebond that couples the diode's anode 110 to the anode side leadframe, at connection point 106. In a typical SOT-23 package, the wirebond will provide for an inductance of approximately 1.5 nH, which is shown by inductance 108. During normal operation, the PIN diode is represented by a series resistance 112 between the diode's anode 110 and cathode 114. Typically, in an SOT-23 package, the cathode 114 of the PIN diode will be directly mounted on the cathode side leadframe which provides for a leadframe inductance 116 between cathode 114 and cathode terminal 118. Leadframe inductance 116 will also have an operational inductance of approximately 0.3 nH.
One of the major problems encountered when designing RF switching circuits (e.g. an antenna switch) with RF switching devices, such as PIN diodes, is the amount of isolation provided by the PIN diodes. In radio communication applications, any increase in the isolation between the receiver and transmitter provided by improved RF switching components utilized in the antenna switch (and other areas) helps improve the overall performance of the radio. A need exists in the art for a way of increasing the isolation provided by RF switching devices without incurring increased cost or part counts.